Several endogenous amino acids including L-glutamate and L-aspartate have potent excitatory effects in the central nervous system. They are thought to act as synaptic transmitters in many neural pathways including those in the spinal cord. Three distinct receptors have been described through which these excitatory amino acids exert their effects. These are referred to as quisqualate, kainate and N-methyl-D-aspartate (NMDA) receptors, after the exogenous excitants most specific for each. In addition, sub-types of the NMDA receptor have been proposed to account for differences observed in the actions of the endogenous excitant quinolinate (2,3-pyridine dicarboxylate) in various regions of the nervous system. The characterization of excitant amino acid receptors has been accomplished primarily using two or more potent antagonists which include D-(-)-2-amino-5-phosphonovalerate (APV), a specific NMDA antagonist, and kynurenate, a compound related to quinolinate which potently attenuates the actions of NMDA- and kainate-like excitants. Structure-activity studies of amino acid receptors were undertaken using standard extracellular recording and iontophoretic techniques in the dorsal horn of the spinal cord in vivo, and compared with the neocortex of the rat. In addition, a spinal cord slice preparation was developed wherein dorso-ventral longitudinal slices were prepared from the lumbar enlargement of weanling rats (50 - 125 g). The slices were maintained in an "interface" tissue bath of novel design. Extracellular recording of several hours duration and up to 8 hours after slice preparation were routinely possible. Conformationally restricted analogues of glutamate, aspartate and quinolinate were examined for agonist and antagonist actions in the rat spinal cord in vivo and in vitro. Compounds found to be excitants were compared directly with quisqualate, kainate, and NMDA for sensitivity to blockade by APV and kynurenate applied both iontophoretically and in the bathing medium; antagonist dose-response curves were constructed for the actions of APV and kynurenate against quisqualate, kainate, quinolinate and NMDA. The conformationally restricted compounds found to be antagonists were examined to determine their potency and specificity against excitations elicited by quisqualate, kainate, quinolinate and NMDA. Although quinolinate is known to be NMDA-like in the hippocampus and cortex, when compared to quisqualate, kainate and NMDA in the spinal cord in vitro, it proved to be unique. A fourth receptor (the "QUIN" receptor) is proposed to account for its actions in the spinal cord. Three of the isomers of 1-amino-1,3-cyclopentane dicarboxylate (ACPD), conformationally restricted analogues of glutamate, were potently blocked by APV and KYNA and were therefore classified as NMDA-like. The fourth, D-trans-ACPD. was indistinguishable from quinolinate in terms of both potency and sensitivity to antagonists. The (-) isomer of trans-1-amino-1,2-cyclopentane dicarboxylate proved to be an antagonist with greater potency against excitations elicited by quisqualate and kainate than those of NMDA. These findings are, in many ways, different from what has been observed in the hippocampal slice. Several pyridine derivatives were examined; 2,5- and 2,6-pyridine dicarboxylate were weak excitants behaving like quisqualate in the presence of APV and kynurenate. No other pyridines were excitatory; however 2,4-pyridine dicarboxylate was observed to be a weak, non-specific antagonist similar in action to acridinate (an antagonist closely related to kynurenate). None of the pyridine derivatives, save quinolinate, are excitatory in the hippocampus. Structural analysis of the active compounds tested, in consideration of previous studies, shows that three points of attachment (two carboxyl and one amino group) are necessary for activation of NMDA, quisqualate and quinolinate receptors in the spinal cord. The location of the distal or y-carboxyl group relative to the a ionic groups appears to be the primary factor determining the activity of a conforrnationally restricted compound. The absolute distance between the Y-carboxyl and α-carbon appears to play a secondary role in determining the action of a compound. / Medicine, Faculty of / Graduate

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Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 215-232). Also available in electronic version.

Synaptic inhibition in the vertebrate central nervous system is largely mediated by type A GABA receptors (GABA(_A)R). The clustering of (GABA(_A)R) at discrete and functionally significant domains on the nerve cell surface is an important determinant in the integration of synaptic inputs. To discern the role that specific GABA(_A)R subunits play in determining the receptor's cell surface topography and mobility, recombinant GABA(_A)Rs, comprising different GABA(_A)R subunit combinations, were transiently expressed in COS7, HEK293 and PC12 cells. In addition, a series of domain swapping experiments were performed in order to elucidate which regions of the protein are important in mobility/anchoring of receptors. The cellular localization and lateral mobility of the recombinantly expressed GABA(_A)Rs were determined by immunocytochemistry and Fluorescence Photobleach Recovery (FPR), respectively. The results presented in this thesis show that GABA(_A)R al subunits are recruited by the β3 subunits from an internally sequestered pool and assembled into a population of GABA(_A)Rs that are spatially segregated into clusters and also immobilised on the cell surface. FPR experiments on recombinant GABA(_A)R containing al-a6 subunits expressed in COS? cells showed restricted mobilities consistent with mobility constants determined for native GABA(_A)Rs expressed on cerebellar granule cells. Furthermore, the intracellular loop domain M3/M4 of the a1 subunits was found to be required for anchoring recombinantly expressed GABA(_A)Rs in C0S7 and cerebellar granule cells in culture, but not for GABA(_A)R clustering at the cell surface.

No description available.

Thesis (Ph. D.)--University of Sydney, 2003. / Title from title screen (viewed Apr. 28, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Dept. of Medicine, Nepean Hospital, Faculty of Medicine. Includes bibliography. Also available in print form.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Title from PDF title page (University of Texas Digital Repository, viewed on September 9, 2009). Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

In the present study non-5-HT₁(A)/non-5-HT₁(C) binding sites in the rabbit caudate nucleus (CN) were examined to determine if they might be identical to the recently discovered 5-HT₁(D) sites in the bovine CN. The characterizations were carried out measuring high-affinity [³H]5-HT binding under conditions where 5-HT₁(A) and 5-HT₁(C) sites were pharmacologically masked in both tissues. Comparison of the pharmacologic profiles of the bovine 5-HT₁(D) and rabbit non-5-HT₁(A)/non-5-HT₁(C) sites revealed similarities, but showed distinct differences. [³H]5-HT binding in the bovine CN was significantly more sensitive to inhibition by GTP than was [³H]5-HT binding in the rabbit CN, and this effect was differentially sensitive to calcium and other divalent cations (i.e., Mg²⁺, Mn²+)⁺in the two tissues. [³H]5-HT binding in the bovine CN was significantly more sensitive to inhibition by NEM than it was in the rabbit CN. Thus, it may be concluded that the non-5-HT₁(A)/non-5-HT₁(C) [³H]5-HT binding sites in rabbit CN are distinct from those in the bovine CN, and we propose that they be tentatively identified as 5-HT₁(R) to distinguish them from the 5-HT₁(D) site.